1. Field of the Invention
The invention relates to a partially implantable hearing device comprising an electro-mechanical output transducer.
2. Description of Related Art
Implantable hearing devices are a class of medical devices for treatment of sensor neural and/or conductive hearing loss of patients who are unable or unwilling to use a conventional hearing aid. The main components of an implantable hearing device are a microphone, an audio signal processing unit, an output transducer for stimulating the user's hearing and a power supply, i.e. a battery. In general, the output transducer may be an electro-mechanical transducer which is used for stimulating a member of the ossicular chain or for directly stimulating the inner ear or which is part of a bone-anchored hearing aid (BAHA), or an electrical stimulator for a cochlear implant, or a combination thereof. If all of these components are implanted, the implantable hearing device is categorized as a fully implantable device. If at least one component remains outside the body, the device is categorized as a partially implantable hearing device; in this case, it requires additional components to transfer power and information between the implanted part and the external part.
Fully implantable devices are beneficial in that they are completely invisible and do not restrict daily activities such as swimming or vigorous movement. However, such devices have to deal with considerable technical challenges related to the implantable microphone which must be biologically stable, which should have low sensitivity to body-generated vibrations such as chewing sounds, and which should not cause feedback squealing by picking-up the output vibration or electrical by-products of the function of the amplifier and transducer. Current fully implantable devices are limited in their available gain, typically due to feedback problems related to either the vibration sensitivity of a microphone covered by a massive layer of skin or to the proximity between the microphone and the output transducer.
A typical design of partially implantable devices has all components except the output transducer outside the body. While this design avoids the microphone challenges of fully implantable devices, it requires large and heavy outside components which are typically held in place by implanted magnets to ensure proper alignment of the implanted and external parts of the transcutaneous link used to transmit power and information into the implanted part of the device. Thus, current partially implantable devices contain bulky, conspicuous external parts, which house the power supply and the audio signal processing electronics, and they are not water-proof, because they contain openings in the housing for access to replaceable batteries, etc. Typically the largest share of the overall power consumption is due to the output transducer. Transcutaneous power transmission is not very efficient, due to technical and physical constraints. Therefore, in conventional partially implantable devices wherein the power source is located outside the body overall power consumption is relatively high, because a significant amount of power is lost in the transcutaneous link, whereby the required size of the power source is increased or the lifetime of the rechargeable or replaceable external battery is reduced.
U.S. Pat. No. 6,620,094 B2 describes a fully implantable hearing device and, as an alternative, a conventional partially implantable hearing device wherein only the electro-mechanical output transducer is implanted, while the external portion comprises the microphone, the audio signal processing electronics and the power source. A further example of a fully implantable hearing device comprising an electro-mechanical transducer is described in U.S. Pat. No. 5,277,694. Also U.S. Pat. No. 6,162,169 relates to a partially or fully implantable hearing device comprising an electro-mechanical output transducer. A further example of a conventional partially implantable hearing device is described in US 2005/0226447 A1.
US 2005/0267549 A1 relates to a cochlear implant device which, according to one embodiment, is a fully implantable device and which, according to an alternative embodiment, is a partially implantable device wherein the implantable part includes the cochlear stimulator, the signal processing electronics and the power source, whereas the external part includes a completely-in-the-canal (CIC)-microphone which is connected to the implantable part via a transcutaneous link.
It is an object of the invention to provide for an implantable hearing device comprising an electro-mechanical output transducer, which device allows for relatively high gain and for comfortable use by the patient.